Generation of hues and saturations in visible spectrum with a broad-spectral white light source has a number of applications including stage lighting. Notably, many colored spotlight projectors use one or more colored optical filters to produce a light of desired hue and saturation by projecting a white light beam through the filters.
Two approaches are usually used to generate colored light. One is to first generate three light beams of three primary additive colors (i.e., red, green, and blue) and then combine them to produce the desired hue and saturation. White light sources can be used to generate three white light beams. These beams subsequently pass through three color filters respectively to obtain color from the three additive primary colors. Dichroic beam combiners, light intensity filters and other optical elements are used to combine the three beams into a single output beam. Adjusting intensities of the three beams in primary colors relative to one another allows the output beam to have various desired hues, saturations, and brightness. One of the disadvantages of such a system is the precise overlapping alignment of the three beams in primary colors is subject to change due to vibrations and other factors. The optical alignment requires frequent maintenance. The optical elements required in this type of system add manufacturing cost.
Another often-used approach uses two or more variable color filters in three subtractive primary colors (i.e., magenta, cyan and yellow) of different saturations to sequentially filter a single white beam, resulting in output light with desired hues and saturations. This approach simplifies the optical alignment using fewer optical elements in comparision with the former approach. In particular, this approach obviates the problem of having three displaced colors in the peripheral region of the output beam present in the former approach.
One key component of the latter approach is implementation of variable color filters, or a color changer based on subtractive primary colors. Many such color changer systems have been developed such as those described in U.S. Pat. Nos. 4,459,014 to Theabult, 4,600,976 to Callahan, 4,745,531 to Leclercq, 4,602,321 to Bornhorst, and 3,260,152 to Aston. However, these prior-art systems have limitations either in uniformity of color filtering or in light intensity handling capacity.
Scrolling color changers use two or more flexible transparencies coated with color changing materials having strong absorption at different selected hues and saturations of color. Different portions of the scrolling transparencies produce different hues and saturations in the light transmitting therethrough. These transparencies work combination to change the color of the output light from a single white light source. This can be understood with the well-known color triangle 100 shown in FIG. 1. The three additive primary colors red, green and blue are represented by the three vertices 102, 104 and 106, respectively. The three subtractive primary colors magenta, yellow and cyan are represented by 122, 124 and 126, respectively. The center 130 of the triangle 100 is the white color. For example, fully saturated red can be achieved by using a filtering portion for fully saturated yellow and a filter portion for fully saturated magenta.
The above-referenced flexible filters made of transparencies having color changing absorbing materials can be made with materials and processes disclosed in the U.S. patent application Ser. No. 08/286,969, disclosure of which is incorporated herein by reference. The flexible tranparent substrates can be polycarbonate, polyestere or polypropylene films. The color changing materials can be a mixture of dye for a particualr color and a polyester binder for holding the dye molecules.
The prior-art scrolling color changers can produce a uniformly filtered output beam and have a wide range of hues and saturations. However, these systems are usually slow and are usually obliged to produce undesired intervening colors in changing from one primary color to another.
One notable prior-art scrolling color changer is disclosed in U.S. Pat. No. 5,126,886 to Richardson et al., the disclosure of which is incorporated herein by reference. The '886 patent uses two or three layers of elongated flexible scrolling substrates coated with light absorbing gels for different subtractive primary colors. In a three-scroll configuration shown in FIG. 2 of the above referenced US patent, each substrate has a surface with a graded portion having a gel of continuously graded concentration along a gradient axis in the elongated direction. The graded distributed gel ranges from a full saturation at one end of the substrate to a total transparent portion at the other end (FIGS. 4, 5, and 6 of the referenced patent). Each substrate corresponds to one subtractive primary color. One drawback of this system is long scrolling time in changing from one primary color (e.g., red) to another (e.g., blue) since at least two of the three substrates have to be scrolled virtually all the way through their respective paths. This can take about two seconds of movement at the full speed operation of a commonly used scrolling motor. Another drawback is the flash of white in the output beam during the above operation along with presence of other intervening colors during the slow scrolling.
The '886 patent further discloses a two-scroll color changer using two dual-hue substrates. The dual-hue substrate combination 200 having a first substrate 210 and a second substrate 220 is illustrated in FIG. 2. The first hue substrate 210 has three sections: a yellow section 12, a transparent portion 214 for white color, and a cyan section 216. The yellow section 212 has a full saturation end portion 213 and the concentration of the absorbing gel for yellow color continuously decreases towards the transparent section 214 along a gradient axis 217 in the elongated direction. The cyan section 216 is similarly constructed, having a full saturation end portion 215 and a continuous decreasing concentration of the absorbing gel for cyan color towards the transparent section 214 along a gradient axis 219. The second hue substrate is similarly constructed with a cyan section 222, a transparent section 224 and a magenta section 226.
The '886 patent's dual-hue configuration still has some of the previously mentioned limitations associated with many of the prior-art scrolling color changers although the flash of white during bumping between primary colors is eliminated. This can be shown in changing the output light from blue to red. Assume that the system initially is set to generate the blue output, thus optic axis 230 being used and both cyan section 216 and magenta section 226 being at the center. An optic axis 234 has to be used to produce the red color. Therefore, the first hue substrate 210 needs to roll almost all the way from one end to the other for changing the output from blue to red. This is a significant duration (e.g., 2 seconds) although no white color is present in the output. However, during the process, the output color goes through other colors in between the red and blue such as magenta as the transparent section 214 of the first substrate scrolls to the center (i.e., optic axis 232 is along the light path).
The present invention describes an improved scrolling color changer system based on a new dual-hue substrate design. In particular, the preferred embodiment of the present invention uses a dual-hue substrate design with five sections and a combination of magenta and yellow in one substrate and a combination of magenta and cyan in another substrate. According to the present invention, the flash of white is eliminated in changing output color between any two primary colors. Importantly, the intervening colors between the two primary colors are eliminated from bumping between any two primary colors. Furthermore, the different color sections in each substrate are designed to minimize the scrolling amount, thus resulting in a high-speed operation that is rarely possible with the prior-art scrolling systems.
The advantages, sophistication, and significance of the present invention will be more apparent in the light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings.